Removing acetylene from ethylene gas streams during polyethylene synthesis

ABSTRACT

Disclosed herein are methods for removing acetylene from an ethylene gas stream wherein a catalyst reacts with the acetylene to polymerize said acetylene forming an ethylene gas stream substantially free of acetylene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 62/907,059, filed on Sep. 27, 2019,the entirety of which is hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with U.S. government support under CHE1565654and 1808234 awarded by the National Science Foundation. The U.S.government has certain rights in the invention.

BACKGROUND

The production of polyethylene from ethylene gas is an importantindustrial process. Acetylene is a common impurity in ethylene feeds andcan act a poison to catalysts in the reaction of ethylene topolyethylene. Most commonly, acetylene is removed via hydrogenation.However, economic efficiency requires high selectivity of the acetylenehydrogenation in the presence of an excess of ethylene to prevent thehydrogenation reaction of ethylene to ethane, thereby killing thereactant. Known catalysts that promote the hydrogenation reaction ofacetylene exhibit activity but possess limited selectivity andstability. Therefore, there is a need for catalysts that can react withacetylene selectively in the presence of excess ethylene producing apure ethylene feed.

SUMMARY

Provided herein are methods of removing acetylene from an ethylene gasstream comprising contacting the gas stream with a catalyst such thatthe catalyst reacts with acetylene to polymerize the acetylene therebyforming an ethylene gas stream substantially free of acetylene; whereinthe catalyst has a structure of

each R¹ is independently Ar¹, C₁-C₂₂ alkyl, or (R³)₃—Si—; each R² isindependently Ar¹, C₃-C₂₂ alkyl, or (R³)₃—Si—; M is W or Mo; Ar¹ is arylor heteroaryl which can be optionally substituted, wherein theheteroaryl is a 5-12 membered aromatic ring comprising from 1 to 4heteroatoms selected from O, N, and S, and the optional substitutionsare 1 to 3 groups independently selected from halo, C₁₋₆ alkyl,OC₁₋₆alkyl, and C₁₋₆haloalkyl; each occurrence of R³ is independentlyC₁-C₂₂ alkyl, Ar¹, —O—(C₁-C₂₂ alkyl), —O—Ar¹, —N—(C₁-C₂₂)₂ alkyl, or—N—Ar¹ ₂; and L is absent or a neutral ligand.

In some embodiments, each R¹ is C₁₋₂₂alkyl. In embodiments, at least oneR¹ is t-butyl. In some cases, each R¹ is t-butyl. In embodiments, atleast one R¹ is Ar¹. In some embodiments, at least one R¹ is phenyl.

In embodiments, each R² is C₁-C₆ alkyl. In some embodiments, each R² ist-butyl.

In embodiments, L is absent. In some cases, L is a neutral ligand. Insome embodiments, L is tetrahydrofuran, Et₂O, thiophene, or pyridine. Inembodiments, L is tetrahydrofuran.

In embodiments, M is W.

In embodiments, the catalyst is in a solution. In some embodiments, thegas stream is bubbled through the solution. In some cases, the ethylenegas stream substantially free of acetylene comprises less than 1% byweight acetylene. In embodiments, ethylene gas stream substantially freeof acetylene comprises less than 0.5% by weight acetylene.

In some embodiments, the acetylene is polymerized at room temperature.In embodiments, the acetylene is polymerized at atmospheric pressure.

In embodiments, the methods herein further comprise reacting theethylene gas stream substantially free of acetylene under polymerizationconditions to form polyethylene.

DETAILED DESCRIPTION

Many modifications and other embodiments will come to mind to oneskilled in the art to which the disclosed compositions and methodspertain having the benefit of the teachings presented herein. Therefore,it is to be understood that the disclosures are not to be limited to thespecific embodiments disclosed and that modifications and otherembodiments are intended to be included within the scope of the appendedclaims.

Disclosed herein are methods of removing acetylene from an ethylene gasstream comprising contacting the gas stream with a catalyst such thatthe catalyst reacts with acetylene to polymerize the acetylene therebyform an ethylene gas stream substantially free of acetylene. Thecatalyst used in the disclosed methods has a structure of

each R¹ is independently Ar¹, C₁-C₂₂ alkyl, or (R³)₃—Si—; each R² isindependently Ar¹, C₃-C₂₂ alkyl, or (R³)₃—Si—; M is W or Mo; Ar¹ is arylor heteroaryl which can be optionally substituted, wherein theheteroaryl is a 5-12 membered aromatic ring comprising from 1 to 4heteroatoms selected from O, N, and S, and the optional substitutionsare 1 to 3 groups independently selected from halo, C₁₋₆ alkyl,OC₁₋₆alkyl, and C₁₋₆haloalkyl; each occurrence of R³ is independentlyC₁-C₂₂ alkyl, Ar¹, —O—(C₁-C₂₂ alkyl), —O—Ar¹, —N—(C₁-C₂₂)₂ alkyl, or—N—Ar¹ ₂; and L is absent or a neutral ligand.

As used herein, and unless specified otherwise, the term “alkyl” refersto straight or branched chain hydrocarbyl groups including from 1 to 22carbon atoms. For instance, an alkyl can have from 1 to 20 carbon atoms,2 to 20 carbon atoms, 2 to 10 carbon atoms, 3 to 5 carbon atoms, or 4 to8 carbon atoms. The term C_(n) means that the alkyl group has “n” carbonatoms. For example, C₄ alkyl refers to an alkyl group that has 4 carbonatoms. C₃₋₂₂alkyl refers to an alkyl group having a number of carbonatoms encompassing the entire range (i.e., 3 to 22 carbon atoms), aswell as all subgroups (e.g., 3-20, 4-11, 3-10, 5-9, 6-8, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, and 22 carbonatoms). Exemplary alkyls include straight chain alkyl groups such asmethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, and the like, and alsoinclude branched chain isomers of straight chain alkyl groups. Thus,alkyl groups include primary alkyl groups, secondary alkyl groups, andtertiary alkyl groups.

As used herein, the term “aryl” refers to monocyclic or polycyclic(e.g., fused bicyclic and fused tricyclic) carbocyclic aromatic ringsystems. Examples of aryl groups include, but are not limited to,phenyl, tolyl, naphthyl, tetrahydronaphthyl, phenanthrenyl,biphenylenyl, indanyl, indenyl, anthracenyl, and fluorenyl. Unlessotherwise indicated, an aryl group can be an unsubstituted aryl group ora substituted aryl group. Some contemplated substitutions include 1 to 3groups independently selected from halo, C₁₋₆ alkyl, OC₁₋₆ alkyl, andC₁₋₆haloalkyl.

As used herein, the term “heteroaryl” refers to a cyclic aromatic ringhaving five to twelve total ring atoms (e.g., a monocyclic aromatic ringwith 5-6 total ring atoms), and containing one to four ring heteroatomsselected from nitrogen, oxygen, and sulfur. Unless otherwise indicated,a heteroaryl group can be unsubstituted or substituted with one or moregroups, and in particular one to four or one to three. In some cases,the heteroaryl group is substituted with one to three groupsindependently selected from halo, C₁₋₆ alkyl, OC₁₋₆ alkyl, andC₁₋₆haloalkyl. Heteroaryl groups can be isolated (e.g., pyridyl) orfused to another heteroaryl group (e.g., purinyl), a cycloalkyl group(e.g., tetrahydroquinolinyl), a heterocycloalkyl group (e.g.,dihydronaphthyridinyl), and/or an aryl group (e.g., benzothiazolyl andquinolyl). Examples of heteroaryl groups include, but are not limitedto, thienyl, furyl, pyridyl, pyrrolyl, oxazolyl, quinolyl, thiophenyl,isoquinolyl, indolyl, triazinyl, triazolyl, isothiazolyl, isoxazolyl,imidazolyl, benzothiazolyl, pyrazinyl, pyrimidinyl, thiazolyl, andthiadiazolyl. When a heteroaryl group is fused to another heteroarylgroup, then each ring can contain five or six total ring atoms and oneto three heteroatoms in its aromatic ring.

As used herein, the term “halo” is defined as fluoro, chloro, bromo, andiodo. The term “haloalkyl” refers to an alkyl group that is substitutedwith at least one halogen, and includes perhalogenated alkyl (i.e., allhydrogen atoms substituted with halogen).

As used herein, the term “neutral ligand” refers to an L-type ligand.L-type ligands are described in detail in Gray L. Spessard and Gary L.Miessler, Organometallic Chemistry, published by Oxford UniversityPress, 2010, for example, page 59. In embodiments, L can compriseN(R³)₃, Ar¹, R³OR³, P(R³)₃, R³CHO, R³COR³, R³COOR³, and S(R³)₂. Inembodiments, L can be N(R³)₃, P(R³)₃, Ar¹, S(R³)₂ or R³OR³. In somecases, L can be selected from the group comprising diethyl ether, methyltert-butyl ether (MTBE), diisopropyl ether, tetrahydrofuran (THF),dioxane and the like. In embodiments, L can be pyridine or derivativesthereof, such as, N,N-dimethylaminopyridine. In embodiments, L cancomprise tetrahydrofuran or substituted tetrahydrofuran, pyridine orsubstituted pyridine, or thiophene or substituted thiophene.

In general, R¹ is independently Ar¹, C₁-C₂₂ alkyl, or (R³)₃—Si—. In somecases, each R¹ can be an alkyl group such as methyl, ethyl, n-propyl,i-propyl, n-butyl, i-butyl, t-butyl, or a larger alkyl group, forexample C₅ to C₂₀ alkyl. In embodiments, each R¹ is independently C₁-C₆alkyl. In embodiments, each R¹ is t-butyl. In embodiments, each R¹ isindependently Ar¹. In general, Ar¹ is a C₆-C₂₂ aryl or 5-12 memberedheteroaryl group comprising 1 to 4 ring heteroatoms selected from O, N,and S, and the optional substitutions are 1 to 3 groups independentlyselected from halo, C₁₋₆ alkyl, OC₁₋₆alkyl, and C₁₋₆haloalkyl. In somecases, Ar¹ comprises pyrrolyl, furanyl, thiophenyl, imidazolyl,pyrazolyl, oxazolyl, isoxazolyl, thiazolyl, phenyl, tolyl, pyridinyl,pyrazinyl, pyrimidinyl, pyridazinyl, or triazinyl. Ar¹ can also be afused aryl or heteroaryl group, including, but not limited to,benzofuranyl, isobenzofuranyl, indolyl, isoindolyl, benzothiophenyl,bensimidazolyl, purinyl, indazolyl, benzoxazolyl, benzisoxazolyl,benzothiazolyl, naphthalenyl, anthracenyl, quinolinyl, isoquinolinyl,quinoxalinyl, acridinyl, quinazolinyl, cinnolinyl, and phthalazinyl. Inembodiments, each R¹ is a phenyl or tolyl.

In embodiments, at least one R¹ comprises C₁-C₆ alkyl. In refinements ofthe foregoing embodiment, the at least one R¹ comprises t-butyl. Inrefinements of the foregoing embodiment, the at least one R¹ comprisesmethyl, ethyl, or isopropyl. In embodiments, at least one R¹ comprisesAr¹. In refinements of the foregoing embodiment, the at least one R¹comprises phenyl or tolyl.

In general, R² is independently Ar¹, C₃-C₂₂ alkyl, or (R³)₃—Si—. In somecases, each R² can be an alkyl group such as n-propyl, isopropyl,n-butyl, i-butyl, t-butyl, or a larger alkyl group, for example C₅ toC₂₀ alkyl. In embodiments, each R² is independently C₃-C₆ alkyl. Inembodiments, each R² is t-butyl. In embodiments, each R² is isopropyl.In embodiments, at least one R² is Ar¹. In embodiments, each R² isindependently Ar¹. In embodiments, at least one R¹ is phenyl or tolyl.In some embodiments, each R² is a phenyl or tolyl.

In embodiments, at least one R² comprises C₃-C₆ alkyl. In someembodiments, at least one R² comprises t-butyl. In some embodiments, atleast one R² comprises isopropyl. In embodiments, at least one R²comprises Ar¹. In some embodiments, at least one R² comprises phenyl ortolyl.

In general, each occurrence of R³ is independently C₁-C₂₂ alkyl, Ar¹,—O—(C₁-C₂₂ alkyl), —O—Ar¹, —N—(C₁-C₂₂)₂ alkyl, or —N—Ar¹ ₂. Inembodiments, each R³ can be an alkyl group such as n-propyl, isopropyl,n-butyl, i-butyl, t-butyl, or a larger alkyl group, for example C₅ toC₂₀ alkyl. In embodiments, each R³ can be selected from C₁-C₆ alkyl. Inembodiments, each R³ is methyl or ethyl. In embodiments, each R³ isisopropyl. In embodiments, each R³ can be Ar¹. In embodiments, at leastone R¹ is phenyl or tolyl. In some embodiments, each R¹ is a phenyl ortolyl.

In embodiments, at least one R³ comprises C₁-C₆ alkyl. In someembodiments, at least one R³ comprises methyl or ethyl. In someembodiments, at least one R³ comprises isopropyl. In embodiments, atleast one R³ comprises Ar¹. In some embodiments, at least one R³ isphenyl or tolyl.

In general, M is W or Mo. In embodiments, M is W.

In embodiments, the catalyst is

The catalyst as described herein can polymerize acetylene selectively inthe presence of ethylene. In embodiments, the catalyst does not reactwith ethylene. It is advantageous to have a catalyst, such as thecatalysts described herein, selectively react with acetylene but notwith ethylene, as this can provides ethylene gas that is substantiallyfree of acetylene.

The methods disclosed herein can comprise contacting the ethylene gasstream, contaminated with acetylene, with a catalyst as disclosed hereinsuch that the catalyst reacts with the acetylene to polymerize theacetylene thereby forming an ethylene gas stream substantially free ofacetylene. The term “substantially free of acetylene” refers to theethylene gas stream having less than 5% by weight acetylene. Inembodiments, the ethylene gas stream substantially free of acetylene cancomprise less than 5% by weight acetylene, or less than 4% by weightacetylene, or less than 3% by weight acetylene, or less than 2% byweight acetylene, or less than 1% by weight acetylene, or less than 0.5%by weight acetylene, or less than 0.1% by weight acetylene, or up to 5%by weight acetylene, or up to 4% by weight acetylene, or up to 3% byweight acetylene, or up to 2% by weight acetylene, or up to 1% by weightacetylene, or up to 0.5% by weight acetylene, or up to 0.1% by weightacetylene.

The methods disclosed herein can comprise a catalyst loading of up to 20mol %. In embodiments, the catalyst loading can be up to 10 mol %, 9 mol%, 8 mol %, 7 mol %, 6 mol %, 5 mol %, 4 mol %, 3 mol %, 2 mol %, 1 mol%, 0.5 mol %, 0.1 mol %, 0.01 mol %, or 0.001 mol %.

In embodiments, the ethylene gas stream, before contacting with thecatalyst, can comprise up to 95% by weight acetylene. In someembodiments, the ethylene gas stream can comprise acetylene in a rangeof 0.1% to 95% by weight, or 1% to 75% by weight, or 50% to 75% byweight, or 1% to 50% by weight, or 5% to 40% by weight, or 0.1% to 30%by weight, or 1% to 20% by weight, or 0.01% to 10% by weight, such as0.1%, 0.5%, 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 75% and 95% by weight.

The methods disclosed herein can comprise the catalyst in solution. Thesolution can comprise a solvent. Examples of solvents that may be usedin the polymerization reaction include organic solvents that are inertunder the polymerization conditions, such as aromatic hydrocarbons,halogenated hydrocarbons, ethers, aliphatic hydrocarbons, or mixturesthereof. In embodiments, the solvent can be benzene, toluene, xylenes,pentane, hexane, methyl t-butyl ether, heptane, 1,4 dioxane, diethylether, 1,2 dichloroethane, or a combination thereof. In embodiments, thesolution can comprise a deuterated solvent. When the catalyst is insolution, the disclosed methods allow for purified ethylene in a facilemanner as well as recyclable use of catalyst, because the polyacetyleneformed is insoluble in the solution and precipitates out, allowing forease of purification and reuse of the catalyst.

In embodiments, the gas stream is bubbled through a solution of thecatalyst such that the catalyst reacts with acetylene to polymerize theacetylene thereby forming an ethylene gas stream substantially free ofacetylene.

The methods as described herein can include reaction temperatures in arange of about −80° C. to about 100° C., about −70 to about 80° C.,about −50° C. to about 75° C., about −25° C. to about 50° C., about 0°C. to about 35° C., about 5° C. to about 30° C., about 10° C. to about25° C., about 15° C. to about 25° C., or about 20° C. to about 25° C.,for example, about 0° C., about 5° C., about 10° C., about 15° C., about20° C., about 25° C., about 30° C., or about 35° C. In embodiments, thetemperature can be room temperature. Reaction times can be instantaneousor in a range of about 30 seconds to about 72 h, about 1 min to about 72h, about 5 min to about 72 h, about 10 min to about 48 h, about 15 minto about 24 h, about 20 min to about 12 h, about 25 min to about 6 h, orabout 30 min to about 3 h, for example, 30 seconds, 1 min, 5 min, 10min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55min, 60 min, 75 min, 90 min, 105 min, 2 h, 3 h, 4 h, 5 h, 6 h, 12 h, 18h, 24 h, 36 h, 48 h, 60 h, or 72 h.

The methods can be carried out at, for example, ambient temperatures indry conditions under an inert atmosphere. In embodiments, the inertatmosphere can comprise N₂ or Ar.

The methods as described herein can be carried out at any suitabletemperature to one of skill in the art. In embodiments, the methods canbe carried out at atmospheric pressure. In embodiments, the methods canbe carried out at pressures of up to 15 psi, for example, 1 psi, 5 psi,6 psi, 7 psi, 8 psi, 9 psi, 10 psi, 11 psi, 12 psi, 13 psi, 14 psi, or15 psi, or in a range of 1 psi to 10 psi, or 1 psi to 5 psi, or 5 psi to15 psi, or 10 psi to 15 psi.

The disclosure herein provides methods of removing acetylene from anethylene gas stream, wherein the catalyst reacts with acetyleneselectively without reacting with ethylene. In embodiments, the catalystpolymerizes acetylene producing a polyacetylene. The reaction of thecatalyst with acetylene to produce polyacetylene can be advantageous, asthe polyacetylene is extremely insoluble and can be separated out of thereaction readily. Therefore the purity of both the catalyst and theethylene gas stream are improved. In embodiments, the polyacetyleneproduced by the reaction of the catalyst with the acetylene in theethylene gas stream can be cyclic.

In embodiments, the method can further comprise the ethylene gas streamsubstantially free of acetylene being further reacted underpolymerization conditions to form polyethylene.

EXAMPLES

Gas stream purification and preparation—Ethylene gas was passed througha cold trap packed with drierite that removed moisture. Acetylene gaswas passed through a cold trap packed with activated carbon and drieritefollowed by a column packed with layers of drierite, activated carbon,and 3 Å sieves. Both purified gases were bubbled into deuterated benzene(C₆D₆) for 3 minutes. This provided the acetylene/C₆D₆ and ethylene/C₆D₆solutions, respectively.

Acetylene Reaction in the presence of ethylene—Two sealable NMR tubeswere charged with a 200 μL of the acetylene/C₆D₆ solution and 140 μL ofthe ethylene/C₆D₆ solution. Into one of the acetylene/ethylene/C₆D₆solution was added 10.0 μL of a C₆D₆ solution of 1 (10 mg/mL). Uponaddition of 1 the solution turned dark blue/black with blackprecipitates formed on the wall of the tube. As a control, an additionof 10.0 μL of a blank C₆D₆ solution to the second NMR tube did notresult in any observable physical changes. The ¹H NMR spectrum of thetube without catalyst 1 revealed the ratio of dissolved acetylene andethylene in the initial mixture solution was 2:1, where acetyleneprotons resonated at 1.34 ppm and ethylene protons resonated at 5.25ppm. The integrations of acetylene and ethylene relative to C₆D₆ was 53%and 25%, respectively. The ¹H NMR of the solution with the addition of 1indicated the catalyst consumed all the acetylene monomer, as theresonance at 1.34 ppm completely disappeared. However, the ethyleneconcentration stayed constant at 25% relative to C₆D₆. The resultingpolyacetylene that forms does not appear in the ¹H NMR spectrum since itis insoluble. This indicated that catalyst 1 selectively polymerizesacetylene in an acetylene/ethylene mixture solution. It also indicatesit can remove acetylene to below the detection limit of the NMR. Thecatalyst (1) used has a structure of

Control Experiment: Only ethylene—Two sealable NMR tubes were chargedwith 400 μL of pure ethylene/C₆D₆ solutions. To the tubes were added a20.0 μL C₆D₆ solution of 1 (10 mg/mL) and 20.0 μL of a blank C₆D₆solution, respectively. Upon addition of 1 the solution turns slightlyyellow due to the color of the complex. The ¹H NMR spectrum of the tubewithout catalyst 1 revealed the integration of dissolved ethylene toC₆D₆ is 23%. The ¹H NMR spectra of the tube after 15 min, 1 h, and 24 hof the addition of 1 revealed that the ethylene concentration remainedconstant (˜22% relative to C₆D₆). The comparison of the ¹H NMR spectrumof 1 and ethylene mixed with 1 after 1 h, the resonance from 1 at 11.65,1.67, 12.4, and 0.96 ppm stayed unchanged in the mixture of ethylene and1, indicating 1 does not polymerize ethylene.

1. A method of removing acetylene from an ethylene gas stream comprisingcontacting the gas stream with a catalyst such that the catalyst reactswith acetylene to polymerize the acetylene thereby forming an ethylenegas stream substantially free of acetylene; wherein the catalyst has astructure of

each R¹ is independently Ar¹, C₁-C₂₂ alkyl, or (R³)₃—Si—; each R² isindependently Ar¹, C₃-C₂₂ alkyl, or (R³)₃—Si—; M is W or Mo; Ar¹ is arylor heteroaryl which can be optionally substituted, wherein theheteroaryl is a 5-12 membered aromatic ring comprising from 1 to 4heteroatoms selected from O, N, and S, and the optional substitutionsare 1 to 3 groups independently selected from halo, C₁₋₆ alkyl, OC₁₋₆alkyl, and C₁₋₆haloalkyl; each occurrence of R³ is independently C₁-C₂₂alkyl, Ar¹, —O—(C₁-C₂₂ alkyl), —O—Ar¹, —N—(C₁-C₂₂)₂ alkyl, or —N—Ar¹ ₂;and L is absent or a neutral ligand.
 2. The method of claim 1, whereineach R¹ is C₁₋₂₂ alkyl.
 3. The method of claim 2, wherein at least oneR¹ is t-butyl.
 4. The method of claim 3, wherein each R¹ is t-butyl. 5.The method of claim 1, wherein at least one R¹ is Ar¹.
 6. The method ofclaim 5, wherein at least one R¹ is phenyl.
 7. The method of claim 1,wherein each R² is C₁-C₆ alkyl.
 8. The method of claim 7, wherein eachR² is t-butyl.
 9. The method of claim 1, wherein L is absent.
 10. Themethod of claim 1, wherein L is a neutral ligand.
 11. The method ofclaim 10, wherein L is tetrahydrofuran, Et₂O, thiophene, or pyridine.12. The method of claim 11, wherein L is tetrahydrofuran.
 13. The methodof claim 1, wherein M is W.
 14. The method of claim 1, wherein thecatalyst is in a solution.
 15. The method of claim 14, wherein the gasstream is bubbled through the solution.
 16. The method of claim 1,wherein the ethylene gas stream substantially free of acetylenecomprises less than 1% by weight acetylene.
 17. The method of claim 16,wherein the ethylene gas stream substantially free of acetylenecomprises less than 0.5% by weight acetylene.
 18. The method of claim 1,wherein the acetylene is polymerized at room temperature.
 19. The methodof claim 1, wherein the acetylene is polymerized at atmosphericpressure.
 20. The method of claim 1, further comprising reacting theethylene gas stream substantially free of acetylene under polymerizationconditions to form polyethylene.